The purpose of the present study was to investigate the viability, growth characteristics and neuropeptide expression of intraocular superior cervical ganglia (SCG) grafts from neonatal (1-3 d), mature (4-5 months) and aged (20-24 months) rats. In vivo measurements, Falck-Hillarp histochemistry using iris whole mounts to assess catecholamine fiber outgrowth and immunocytochemical localization of tyrosine hydroxylase (TH-), neuropeptide Y (NPY-), leu-enkephalin (ENK-) and calcitonin gene-related peptide (CGRP-) like immunoreactivity (LI) were used. Measurements indicated a marked decrease in volume during the first week after grafting and a more gradual decrease thereafter. This was most evident in newborn SCG. With prolonged survival time, the newborn ganglia demonstrated more varicose nerve terminals and increased catecholamine fiber outgrowth and arborization. Extensive and complex outgrowth of catecholamine fibers with varicose nerve terminals occurred more rapidly with mature and aged ganglia. In situ, all ganglion cell bodies and fibers demonstrated TH-LI. Localization of TH-LI after grafting indicated an increase in fiber density and a decrease in cell body density of 65%, 40% and 40% in newborn, mature and aged ganglia respectively. NPY-LI in cell bodies had a perinuclear fluorescence pattern consistent with localization in the Golgi apparatus. Grafting of newborn, mature and aged SCG resulted in a 20%, 20% and 35% decrease respectively of cell bodies containing NPY-LI. A concommitant increase in fiber diameter, fluorescence intensity and extent of arborization was observed. The characteristic distribution of ENK-LI in cell bodies and axons in mature and aged ganglia was not affected by grafting. However, there was a greater than 50% reduction in the number of cell bodies expressing ENK-LI. CGRP-LI, localized in fibers and axon terminals in SCG in situ, was not identified after grafting. In summary, we have demonstrated that SCG from all age groups form extensive fiber networks and continue neuropeptide expression after intraocular grafting. This was seen best in mature and aged donors and may suggest a role for SCG transplants in the replacement of monoaminergic neurons in the CNS.